1. Field of the Invention
The present invention relates to plasma display panels including crystalline films that are formed to cover uneven surfaces and are exposed to discharge gas spaces.
2. Description of the Related Art
An AC type plasma display panel includes a dielectric layer for covering display electrodes. The dielectric layer is formed on a substrate on which the display electrodes are arranged in a manner to extend over the entire screen. The dielectric layer that is made of low melting point glass, which is a general material, has a thickness of approximately 20 μm to 30 μm. A protection film is deposited on a surface of the dielectric layer. The protection film has a thickness of approximately 0.5 μm to 1 μm and serves to prevent sputtering due to discharges for the dielectric layer. Stated differently, the display electrodes are covered with a layered film including the dielectric layer and the protection film for a discharge gas space. The layered film including the dielectric layer and the protection film is herein referred to as an insulation layer.
Magnesium oxide (magnesia: MgO) is used as a material for the protection film. Magnesia is an insulation material having a high secondary electron emission coefficient. The protection film made from magnesia is exposed to the discharge gas space. Thereby, a discharge starting voltage is reduced, which facilitates generation of discharges. A vacuum deposition method, which is a proven method industrially, is used for forming the protection film made from magnesia.
A vapor deposition method (also called a vapor growth method) has recently received attention as a method for forming dielectric layers. Japanese unexamined patent publication No. 2000-21304 describes forming a dielectric layer made from silicon dioxide or organic silicon oxide using plasma CVD (Chemical Vapor Deposition) that is one kind of chemical vapor deposition method. The vapor deposition method enables provision of a thin dielectric layer having a uniform thickness. Further, the vapor deposition method makes it possible to form a dielectric layer with a low relative dielectric constant that is favorable to reduction of interelectrode capacitance at temperatures lower than a burning temperature of low melting point glass.
Layers obtained by the vapor deposition method have a structural feature in which a surface is uneven due to reflection of irregularities of a foundation surface (a surface on which layers are formed). More specifically, surfaces of layers obtained by the vapor deposition method are not even unlike a surface of a low melting point glass layer that is burned at sufficiently high temperatures. A dielectric layer is formed on a substrate on which display electrodes are arranged. Accordingly, a dielectric layer obtained by the vapor deposition method has an uneven surface in which portions corresponding to the display electrodes bulge out compared to the other portions by amounts corresponding to the thickness of the display electrodes. Since a protection film formed on the uneven surface is sufficiently thin, the surface of the protection film, i.e., a surface of an insulation layer is similarly uneven.
Japanese unexamined patent publication No. 2003-308784 suggests using gaps provided by irregularities on an insulation layer surface as air passages for prompt replacement of the inside air and a discharge gas in the case of manufacture of plasma display panels. The patent publication describes an internal structure in which projections of the insulation layer on a first substrate abut against a mesh-patterned partition supported by a second substrate.
In plasma display panels in which insulation layers for covering electrodes have uneven surfaces, a problem arises that an operating life for enabling a desired display quality is short compared to plasma display panels in which insulation layers have even surfaces.